The Delayed Coking Process

The reduced crude or vacuum resid enters the coke fractionator bottom surge zone (see Figure 6-1). The feed is mixed with recycle condensed in the bottom section of the fractionator and pumped by heater charge pump P-04 through coke heater H-01, where the charge is rapidly heated to the desired temperature for coke formation in the coke drums. Steam is injected in each heater coil to maintain the required minimum velocity and residence time and suppress the formation of coke in the heater coils.

Coking Process Refinery

Figure 6-1. Delayed coker unit. C.W. = cooling water; SV = coker switch value;

Figure 6-1. Delayed coker unit. C.W. = cooling water; SV = coker switch value;

The vapor/liquid mixture leaving the furnace enters coke drums V-01 or V-02, where the trapped liquid is converted into coke and light hydrocarbon vapors. The vapors make their way through the drum and exit it. A minimum of two drums are required for operation. One drum receives the furnace effluent, which it converts into coke and gas, while the other drum is being decoked.

The coke overhead vapors flow to the coker fractionator and enter below the shed section. The coke drum effluent vapors are quenched with fresh feed then washed with hot gas oil pumpback in the wash section trays. These operations clean and cool the effluent product vapors and condense a recycled stream at the same time. This recycled stream, together with fresh feed, is pumped from the coker fractionator to the coker furnace. The washed vapor passes through the rectifying section of the tower. A circulating heavy gas oil pumparound stream withdrawn from the pumparound pan is used to remove heat from the tower, condensing a major portion of the heavy gas oil and cooling the ascending vapors. The hot pumparound stream of heavy gas oil withdrawn from the fractionator is used for steam generation. The heavy gas/oil product is partially cooled via exchange with steam generation then with an air cooler to storage temperature. The light gas/oil product is steam stripped for removal of light ends, partially cooled via steam generation and air cooled to storage temperature.

Lean sponge oil is withdrawn from the fractionator and cooled by heat exchange with rich sponge oil, then air cooled, before flowing to the top of the sponge absorber. Rich sponge oil is returned to the fractionator after preheat by exchange with lean sponge oil.

The overhead vapors are partially condensed in fractionator overhead condenser before flowing to the fractionator overhead drum. The vapor is separated from the liquid in this drum. The vapor flows under pressure control to the suction of the gas compressor in the gas recovery section. The top of the fractionator is refluxed with part of the condensed hydrocarbon liquid collected in the overhead drum. The balance of this liquid is sent with the vapors to the gas recovery plant. Sour water is withdrawn from the overhead drum and pumped to off-site treating facilities.

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Responses

  • brian
    How is sponge coke broken down into dust form?
    3 years ago

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